Scalloped surface turbine stage with purge trough

ABSTRACT

A turbine stage includes a row of airfoils joined to corresponding platforms to define flow passages therebetween. Each airfoil includes opposite pressure and suction sides and extends in chord between opposite leading and trailing edges. Each platform has a scalloped flow surface including a purge trough commencing tangentially in a blend area of the platform. The purge trough extending axially toward the suction side of the airfoil, aft of the leading edge, to channel a purge flow.

BACKGROUND

The present disclosure relates generally to gas turbine engines, anyturbomachinery, and, more specifically, to turbines therein.

In a gas turbine engine air is pressurized in a compressor and mixedwith fuel in a combustor for generating hot combustion gases. Turbinestages extract energy from the combustion gases to power the compressor,while also powering an upstream fan in a turbofan aircraft engineapplication, or powering an external drive shaft for marine andindustrial applications.

A high pressure turbine (HPT) immediately follows the combustor andincludes a stationary turbine nozzle which discharges combustion gasesinto a row of rotating first stage turbine rotor blades extendingradially outwardly from a supporting rotor disk. The HPT may include oneor more stages of rotor blades and corresponding turbine nozzles.

Following the HPT is a low pressure turbine (LPT) which typicallyincludes multiple stages of rotor blades and corresponding turbinenozzles.

Each turbine nozzle includes a row of stator vanes having radially outerand inner endwalls in the form of arcuate bands which support the vanes.Correspondingly, the turbine rotor blades include airfoils integrallyjoined to radially inner endwalls or platforms supported in turn bycorresponding dovetails which provide mounting of the individual bladesin dovetail slots formed in the perimeter of the supporting rotor disk.An annular shroud surrounds the radially outer tips of the rotorairfoils in each turbine stage.

The stator vanes and rotor blades have corresponding airfoils includinggenerally concave pressure sides and generally convex suction sidesextending axially in chord between opposite leading and trailing edges.Adjacent vanes and adjacent blades form corresponding flow passagestherebetween bound by the radially inner and outer endwalls.

During operation, combustion gases are discharged from the combustor andflow axially downstream as a core flow through the respective flowpassages defined between the stator vanes and rotor blades. In addition,purge air from a purge cavity existing upstream of the airfoil leadingedge is discharged as a purge flow that prevents ingesting hot core flowbelow the main gas path and potentially provides a cooling effect to theplatforms and airfoils. The aerodynamic contours of the vanes andblades, and corresponding flow passages therebetween, are preciselyconfigured for maximizing energy extraction from the combustion gaseswhich in turn rotate the rotor from which the blades extend.

The complex three-dimensional (3D) configuration of the vane and bladeairfoils is tailored for maximizing efficiency of operation, and variesradially in span along the airfoils as well as axially along the chordsof the airfoils between the leading and trailing edges. Accordingly, thevelocity and pressure distributions of the combustion gases and purgeair over the airfoil surfaces as well as within the corresponding flowpassages also vary.

Undesirable pressure losses in the combustion gas flowpaths thereforecorrespond with undesirable reduction in turbine aerodynamics andoverall turbine efficiency. For example, the combustion gases enter thecorresponding rows of vanes and blades in the flow passages therebetweenand are necessarily split at the respective leading edges of theairfoils. In addition, mixing of the purge air flow and the core flowmay lead to turbine inefficiency.

The locus of stagnation points of the incident combustion gases extendsalong the leading edge of each airfoil, and corresponding boundarylayers are formed along the pressure and suction sides of each airfoil,as well as along each radially outer and inner endwall whichcollectively bound the four sides of each flow passage. In the boundarylayers, the local velocity of the combustion gases varies from zeroalong the endwalls and airfoil surfaces to the unrestrained velocity inthe combustion gases where the boundary layers terminate.

Turbine losses can occur from a variety of sources, for example,secondary flows, shock loss mechanism and mixing losses. One commonsource of turbine pressure losses is the formation of horseshoe vorticesgenerated as the combustion gases are split in their travel around theairfoil leading edges. A total pressure gradient is affected in theboundary layer flow at the junction of the leading edge and endwalls ofthe airfoil. This pressure gradient at the airfoil leading edges forms apair of counterrotating horseshoe vortices which travel downstream onthe opposite sides of each airfoil near the endwall. The two vorticestravel aft along the opposite pressure and suction sides of each airfoiland behave differently due to the different pressure and velocitydistributions therealong. For example, computational analysis indicatesthat the suction side vortex migrates away from the endwall toward theairfoil trailing edge and then interacts following the airfoil trailingedge with the pressure side vortex flowing aft thereto.

The interaction of the pressure and suction side vortices occurs nearthe midspan region of the airfoils and creates total pressure loss and acorresponding reduction in turbine efficiency. These vortices alsocreate turbulence and increase undesirable heating of the endwalls.

Since the horseshoe vortices are formed at the junctions of turbinerotor blades and their integral root platforms, as well at the junctionsof nozzle stator vanes and their outer and inner bands, correspondinglosses in turbine efficiency are created, as well as additional heatingof the corresponding endwall components.

Similarly, cross-passage pressure gradients between the pressure andsuction side of the blade give rise to secondary flow structures andvortices that alter the desired aerodynamics of the blade, giving riseto losses in turbine efficiency as well as possible heating of theendwalls and even the blade.

At the leading edges of the turbine blades, and more particularly at ajunction of the leading edge and the leading edge purge cavity,secondary flow structures and mixing of a purge flow from the leadingedge purge cavity, results in mixing losses. In addition, the secondaryflow structures result in mixing of the purge flow with the main coreflow, resulting in a trajectory of the purge flow that is remote fromthe platform. These secondary flow structures result in high heatconcentrations in the area where the turbine blade join the bladeendwall structure.

Accordingly, it is desired to provide an improved turbine stage forreducing horseshoe and secondary flow vortex affects, as well asincreasing aerodynamic loading while controlling heat distribution andefficiency or improving efficiency and thermal loading while maintainingaerodynamic loading and/or torque production.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment, disclosed is a scallopedsurface turbine stage with a purge trough. The turbine stage comprisinga row of airfoils integrally joined to corresponding platforms andspaced laterally apart to define respective flow passages therebetweenfor channeling gases. Each of the flow passage having a width. Each ofsaid airfoils including a concave pressure side and a laterally oppositeconvex suction side extending in chord between opposite leading andtrailing edges. At least some of said platforms having a scalloped flowsurface including a purge trough extending tangentially into a blendarea and at least a portion of a purge cavity wall of the platform andextending axially toward the suction side of the airfoil, aft of theleading edge, to channel a purge flow.

In accordance with another exemplary embodiment, disclosed is ascalloped surface turbine stage with a purge trough. The turbine stagecomprising a row of airfoils integrally joined to correspondingplatforms and spaced laterally apart to define respective flow passagestherebetween for channeling gases. Each of the flow passages having adefined width. Each of said airfoils including a concave pressure sideand a laterally opposite convex suction side extending in chord betweenopposite leading and trailing edges. At least some of said platformshaving a scalloped flow surface including a purge trough extendingtangentially into a blend area and at least a portion of a purge cavitywall of the platform, a bulge adjoining said pressure side aft of saidleading edge, and a bowl adjoining said purge trough and said suctionside aft of said leading edge of said respective airfoils. The purgetrough extending axially toward the suction side of the airfoil to blendwith the bowl and channel a purge flow.

In accordance with yet another exemplary embodiment, disclosed is ascalloped surface turbine stage with a purge trough. The turbine stagecomprising a turbine blade. The turbine blade comprising an airfoilintegrally joined to a platform, and having laterally opposite pressureand suction sides extending in chord between axially opposite leadingand trailing edges. The platform including a purge trough extendingtangentially into a blend area and at least a portion of a purge cavitywall of the platform. The purge trough extending axially toward thesuction side of the airfoil, aft of the leading edge, to channel a purgeflow.

Other objects and advantages of the present disclosure will becomeapparent upon reading the following detailed description and theappended claims with reference to the accompanying drawings. These andother features and improvements of the present application will becomeapparent to one of ordinary skill in the art upon review of thefollowing detailed description when taken in conjunction with theseveral drawings and the appended claims.

DRAWINGS

The above and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a forward-facing-aft elevational view of exemplary turbineblades in a turbine stage row according to an embodiment;

FIG. 2 is a planiform sectional view through the blades illustrated inFIG. 1 and taken along line 2-2 of FIG. 1 according to an embodiment;

FIG. 3 is a isometric view of the suction side of the blades illustratedin FIG. 1 according to an embodiment;

FIG. 4 is an isometric view of the pressure side of the bladesillustrated in FIG. 1 according to an embodiment;

FIG. 5 is a isometric view aft-facing-forward of the blades illustratedin FIG. 1 according to an embodiment;

FIG. 6 is a forward-facing-aft elevational view of exemplary turbineblades in a turbine stage row according to another embodiment; and

FIG. 7 is a planiform sectional view through the blades illustrated inFIG. 6 and taken along line 7-7 of FIG. 6 according to an embodiment.

DETAILED DESCRIPTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, illustrated in FIG. 1are two exemplary first stage turbine rotor blades 10 whichcircumferentially adjoin each other in a full row thereof in acorresponding turbine stage of a gas turbine engine. As indicated above,combustion gases 12 are formed in a conventional combustor (not shown)and discharged in the axial downstream direction through the row ofturbine blades 10 as a core flow 13. The turbine blades 10 extractenergy from the combustion gases 12 for powering a supporting rotor disk(not shown) on which the blades 10 are mounted.

The turbine stage includes a complete row of the blades 10, with eachblade 10 having a corresponding airfoil 14 integrally joined at a rootend to a corresponding radially inner endwall or platform 16. Eachplatform 16 is in turn integrally joined to a corresponding axial-entrydovetail 18 conventionally configured for supporting the correspondingturbine blade 10 in the perimeter of the rotor disk.

Each airfoil 14 includes a generally concave pressure side 20 and acircumferentially or laterally opposite, generally convex suction side22 extending axially in chord between opposite leading and trailingedges 24, 26, respectively. The two edges 24, 26 extend radially in spanfrom root to tip of the airfoil 14.

As shown in FIGS. 1 and 2, each airfoil 14 may be hollow and include aninternal cooling circuit 28 bound by the opposite pressure and suctionsides 20, 22. The cooling circuit 28 may have any conventionalconfiguration and includes inlet channels extending through the platform16 and dovetail 18 for receiving cooling air 30 bled from the compressorof the engine (not shown).

The cooling air 30 is typically discharged from each airfoil 14 throughseveral rows of film cooling holes 32 located where desired on thepressure and suction sides 20, 22 of the airfoil 14, and typicallyconcentrated near the leading edge 24 thereof. Each airfoil 14 typicallyalso includes a row of trailing edge cooling holes 34 which emergethrough the pressure side 20 of the airfoil 14 just before the thintrailing edge 26 thereof.

The exemplary turbine blades 10 illustrated in FIGS. 1 and 2 may haveany conventional configuration of the airfoil 14, platform 16, anddovetail 18 for extracting energy from the combustion gases 12 duringoperation. As indicated above, the platform 16 is integrally joined tothe root end of the airfoil 14 and defines the radially inner flowboundary for the combustion gases 12, or the core flow 13.

The blades 10 are mounted in a row around the perimeter of the rotordisk, with the adjacent airfoils 14 being spaced circumferentially orlaterally apart to define therebetween flow passages 36 having a passagewidth “x” defined between adjacent leading edges 24 (as best illustratedin FIG. 2) for channeling the combustion gases 12 and a purge flow 15 ofpurge air from a purge flow cavity (not shown) axially in the downstreamdirection during operation.

Each inter-airfoil flow passage 36 in the turbine stage illustrated inFIGS. 1 and 2 is therefore defined and bounded by the pressure side 20of one airfoil 14, the suction side 22 of the next adjacent airfoil 14,the corresponding pressure and suction side portions 20, 22 of theadjacent platforms 16, and the radially outer turbine shroud (not shown)which surrounds the radially outer tip ends of the airfoils 14 in thecomplete row of turbine blades 10.

As indicated above in the Background section, the combustion gases 12flow through the corresponding flow passages 36 as the core flow 13during operation and are necessarily split by the individual airfoils14. The high velocity combustion gases are circumferentially split atthe corresponding airfoil leading edges 24 with a stagnation pressurethereat, and with the formation of corresponding boundary layers alongthe opposite pressure and suction sides 20, 22 of the airfoil 14.Furthermore, the combustion gases 12 also form a boundary layer alongthe individual blade platforms 16 as the gases are split around theairfoil leading edge 24 at its juncture with the platform 16.

In addition, the purge air flows from the purge flow cavity existingupstream of the airfoils 14 through the corresponding flow passages 36as the purge flow 15. Minimizing an ejection of the purge flow 15 as apercentage of the core flow 13 leads to an increase of the staticpressure downstream of the airfoil 14. This effect contributes to movethe trailing edge 26 shock upstream, thus decreasing the trailing edgeloss in the airfoils 14.

The split core flow 13 along the blade platforms 16 results in a pair ofcounterrotating horseshoe vortices which flow axially downstream throughthe flow passages 36 along the opposite pressure and suction sides 20,22 of each airfoil 14. These horseshoe vortices create turbulence in theboundary layers, and migrate radially outwardly toward the mid-spanregions of the airfoils 14 and create losses of total pressure andreduce turbine efficiency. The horseshoe vortices are energized by thepresence of the purge cavity and purge flow 15 which modify thecross-passage static pressure gradient.

The exemplary turbine rotor stage illustrated in FIG. 1 may have anyconventional configuration such as that specifically designed as a firststage HPT rotor for extracting energy from the combustion gases 12 topower the compressor in a typical manner. As illustrated, the incidentcombustion gases 12 are split along the airfoil leading edges 24 to flowaxially through the corresponding flow passages 36 as the core flow 13in the downstream direction while the incident purge air flows across ashoulder area, or blend area, 40 of the platforms 16, wherein the blendarea 40 is defined as the radius between a purge cavity wall 41 and theplatform 16 surface. The purge air flows and mixes with the core flow 13to flow axially through the corresponding flow passages 36 as the purgeflow 15 in the downstream direction.

The concave profile of the pressure sides 20 and the convex profile ofthe suction sides 22 are specifically configured for effecting differentvelocity and pressure distributions for maximizing extraction of energyfrom the combustion gases 12. The platforms 16 define radially innerendwalls which bound the combustion gases 12, with the gases also beingbound radially outwardly by a surrounding turbine shroud (not shown).

In the illustrated configuration, the incident combustion gases 12 atthe junction of the platforms 16 and leading edges 24 are subject to thehorseshoe vortices, fueled by modifying of the cross-passage staticpressure gradient by the purge flow 15. The combustion gases 12 progressthrough the flow passages 36 along the opposite pressure 20 and suctionsides 22 of the airfoils 14. As indicated above, these vortices createturbulence, decrease the aerodynamic efficiency of the turbine stage,and increase the heat transfer heating of the platforms 16.

Accordingly, the platforms 16 illustrated initially in FIG. 1 arespecifically configured with scalloped or contoured flow surfaces thatminimize mixing of the purge flow 15 with the core flow 13 to minimizelosses and bound the combustion gases 12 to reduce the strength of thehorseshoe vortices. A first exemplary configuration of the scallopedplatforms 16 is shown generally in FIG. 1 with isoclines of commonelevation from a nominally axisymmetric platform. FIG. 2 illustrates inmore detail the isoclines of FIG. 1 in planiform view. A secondexemplary configuration of the scalloped platforms 16 is shown generallyin FIG. 6 and FIG. 7 illustrating isoclines of common elevation from anominally axisymmetric platform and a more detailed illustration of theisoclines in planiform view, respectively.

Referring more specifically to FIGS. 1 and 2, modern computational fluiddynamics have been used to study and define the specific 3D contours ofthe platforms 16 for weakening the horseshoe vortices and minimizingmixing of the purge flow 15 with the core flow 13 and ingestion into thepurge cavity, while correspondingly improving turbine aerodynamicefficiency. The scalloped platforms 16 illustrated in FIGS. 1 and 2include a scallop or a purge trough 38 configured to extend into theblend area 40 and at least a portion of a purge cavity wall 41 of theplatform 16, having a lower elevation (−) relative to a nominalaxisymmetric platform surface of a conventional platform that definesthe reference zero (0) surface and forming a depression or troughtherein that modifies the blend area 40 and at least a portion of thewall cavity 41. In the illustrated embodiment, the purge trough 38 isformed tangentially in the blend area 40 and extending into the purgewall cavity 41 having a maximum depth location approximately midway thepassage 36 width “x”, between the leading edges 24 of adjacent airfoils14 may extend in a lateral direction approximately 60% the passage 38width “x”. In an alternate embodiment, the purge trough 38 may be formedtangentially in the blend area 40 and extending into at least a portionof the purge wall cavity 41 and having a maximum depth location anywherebetween −10%-60% of the passage 36 width “x” between the leading edges24 of adjacent airfoils 14, wherein such measurement is measuredcommencing from the leading edge 24 of a first airfoil 14 toward thesuction side 22 of the first airfoil 14 and extending toward the leadingedge 24 of a second adjacent airfoil 14 at the pressure side 20. In anembodiment, the purge trough 38 may extend in a lateral directionapproximately 60% the passage 38 width “x”. In yet another embodiment,the purge trough 38 may be formed substantially tangentially in theblend area 40 and extending into at least a portion of the purge wallcavity 41 and having a maximum depth location anywhere between −10%-60%of the passage 36 width “x” between the leading edges 24 of adjacentairfoils 14 as previously described, and located at a position axiallydownstream of the leading edges 24 and within the passage 36 formedtherebetween.

The purge trough 38 is configured to modify the blend area 40 and atleast a portion of the purge cavity wall 41 of the airfoil 14 to easethe purge flow 15 into the core flow 13. More specifically, the purgetrough 38 is configured to maintain a trajectory of the purge flow 15closer to the platform 16 on the suction side 22 to minimize asubsequent downwash of the hot core flow 13 on the pressure side 20 ofthe airfoil 14 to backfill with fluid. The purge trough 38 and purgeflow 15 serve to modify the cross passage static pressure gradient whichenergizes the horseshoe vortices.

Additionally, the presence of the purge trough 38 allows for themanipulation of the operational thermal profile at the leading edge 24of the airfoil 14. This is because the modification in the purge flow 15can change or cause a reduction of convective mixing and/or heattransfer which can normally bring the core flow 13 in contact with theendwalls. This aspect of the present disclosure allows for manipulationof the thermal profile via the reduction in mixing of the purge flow 15with the core flow 13. Thus, a desired thermal distribution can beattained and can be optimized, resulting in a reduction of the coolingrequired.

In an embodiment, an optional local bump or bulge 46 may be included inaddition to the purge trough 38, rising upwardly (+) into the flowpassage 36 relative to the nominal axisymmetric reference surface (θ).In addition, in yet another embodiment, an integral gouge or bowl 48 maybe included in addition to the purge trough 38 that has a lowerelevation (−) relative to the nominal axisymmetric platform surface (θ)to form a depression therein. In yet still another embodiment, a bulge46 and a bowl 48 may be included in addition to the purge trough 38.

It is noted that the specific sizes and spacing of the airfoils 14 areselected for a particular engine design and mass flow rate therethrough.The arcuate sidewalls of the airfoils 14 typically define a flow passage36 circumferentially therebetween that converges in the axial downstreamdirection from the leading edges 24 to the trailing edges 26.

The trailing edge 26 of one airfoil 14 typically forms a throat ofminimum flow area along its perpendicular intersection near the midchordof the suction side 22 of an adjacent airfoil 14. The flow area of theflow passage 36, including the minimum flow area of the throat thereof,are preselected for a given engine application and therefore arecontrolled by both the radially inner endwall defined by platform 16, aswell as the radially outer endwalls defined by the turbine shroud (notillustrated).

The reference platform surface may therefore be conveniently defined asthe conventional axisymmetrical surface defined by circular arcs aroundthe circumference of the turbine stage, and may be used as the zeroreference elevation illustrated in FIG. 2. In an embodiment including apurge trough 38, a bulge 46 and a bowl 48, the bulge 46 rises outwardlyin elevation (+) from the zero reference plane or surface, whereas thepurge trough 38 and the bowl 48 extend in depth (−) below the referenceplane or surface. In this way, the trough 38, bulge 46 and bowl 48 maycomplement and offset each other for maintaining the desired or givenflow area for each flow passage 36.

The purge troughs 38, bulges 46 and bowls 48 illustrated in FIGS. 1 and2 are preferentially located specifically for reducing the strength ofthe horseshoe vortices, minimizing losses due to secondary flows,minimizing mixing of the purge flow 15 from a leading edge purge cavitywith the main core flow 13, minimizing the ingestion of the hot coreflow into the purge cavity, and modifying the cross passage staticpressure gradient which energizes the horseshoe vortexes, all improvingturbine aerodynamic efficiency. In the illustrated embodiment, the purgetrough 38 is configured at a position proximate the leading edge 24 atthe suction side 22 and is formed to extend onto the shoulder, or blendarea 40, of the platform 16. The bulge 46 is configured to directlyadjoin the airfoil pressure side 20 at a position downstream, or aft, ofthe leading edge 24. The bowl 48 is configured to directly adjoin thepurge trough 38 and the airfoil suction side 22 aft of the leading edge24.

By using the purge trough 38, the purge flow 15 is eased into the coreflow 13, with the trajectory of the purge flow 15 maintained closer tothe platform 16 as it lifts off the platform 16 on the suction side 22.This minimizes a subsequent downwash of hot core flow 13 on the pressureside 20. The result is a less mixed fluid flow exiting the flow passages36.

By incorporating the leading edge bulge 46 and bowl 48 into anembodiment including the purge trough 38, the incoming horseshoevortices can be offset by local streamline curvature of the combustiongases 12 around the bulge 46. Correspondingly, the radially outwardmigration of the horseshoe vortices can be interrupted early in the flowpassage 36 by the bowl 48.

As previously eluded to, the purge trough 38 is effective for changingthe local stagnation point at the root of the airfoil, guiding the purgeflow into the core flow thereby controlling the amount of mixing thatoccurs, as well as controlling the trajectory of the purge flow and itssubsequent merging with the suction side leg of the horseshoe vortex.

When included, the bulge 46 and the bowl 48 are effective for reducingflow acceleration of the combustion gases 12, increasing local staticpressure, altering gradients in gas pressure, reducing vortexstretching, and reducing reorientation of the horseshoe vortices as theytravel downstream through the flow passages 36. These combined effectslimit the ability of the horseshoe vortices to migrate radiallyoutwardly along the airfoil suction side 22, and reduce the vortexstrength and in turn increasing overall efficiency of the turbine stage.

As indicated above, FIG. 2 is a planiform view of the platforms 16 withisoclines of equal elevation relative to the reference zero surface.FIG. 3 illustrates the platforms 16 in isometric view with superimposedsurface gradient lines to emphasize the 3D varying contour of theplatforms 16 between the forward and aft ends of each platform 16 andcircumferentially or laterally between adjacent airfoils 14.

Since the platforms 16 extend on both sides of each airfoil 14,typically with small extensions forward of the leading edge 24 and aftof the trailing edge 26, the purge trough 38, the elevated bulge 46 andthe depressed bowl 48 will smoothly transition with each other in apreferred manner to minimize mixing of the purge flow 15 and reduce thestrength of the horseshoe vortices. Preferably, the bulge 46 decreasesin height or elevation as it extends aft and laterally along thepressure side 20 to join the bowl 48 along the suction side 22 and thepurge trough 38 extends into the blend area 40 of the platform 16 towardthe purge cavity. The bowl 48 extends along the suction side 22 betweenthe leading and trailing edges 24, 26, commencing, for example, near theleading edge 24 and blending with the purge trough 38 and terminatingapproximately mid-way the airfoil 14 toward the trailing edge 26.

FIGS. 2-4 best illustrate that the purge trough 38 is configuredlaterally off-centered with maximum depth at the suction side 22 forwardthe leading edge 24 so as to extend into the blend area 40 of theplatform 16. The purge trough 38 further blends into the bowl 48 aft ofthe leading edge 24.

FIGS. 2 and 4 best illustrate that the bulge 46 is centered with maximumheight at the pressure side 20 of the airfoil 14, aft of the leadingedge 24, and decreases in height aft of the leading edge 24 and towardsthe trailing edge 26, as well as laterally or circumferentially from thepressure side 20 of one airfoil 14 toward the suction side 22 of thenext adjacent airfoil 14.

FIGS. 2 and 5 best illustrate that the bowl 48 is centered with maximumdepth at the suction side 22 near the maximum lateral thickness of eachairfoil in its hump region, and blends aft of the leading edge 24 intothe purge trough 38, while decreasing in depth towards the trailing edge26, as well as laterally or circumferentially from the suction side 22of one airfoil 14 towards the pressure side 20 of the next adjacentairfoil 14 where it blends with the elevated bulge 46.

FIG. 4 illustrates schematically the incident combustion gases 12 whichhave a corresponding boundary layer in which the velocity of thecombustion gases 12 is zero directly at the flow surface of the platform16 and increases rapidly to the freestream velocity. The thickness ofthe boundary layer ranges from about two percent to about 15 percent ofthe radial height or span of the airfoil 14. In addition, illustrated isthe incident purge flow 15 upon the purge trough 38. The magnitude ofthe platform scalloping, encompassing the purge trough 38, and theoptional bulge 46 and bowl 48, can be relatively small to specificallyminimize losses due to secondary flows, minimize mixing of the purgeflow 15 with the core flow 13 and reduce the strength of the horseshoevortices to increase turbine aerodynamic efficiency.

The purge trough 38 as shown in FIGS. 2 and 4 has a maximum depth whichmay scale with the purge flow level. The bulge 46 as shown in FIGS. 2and 4 has a maximum height which is generally equal to the thickness ofthe incoming boundary layer of combustion gases 12 as they are firstchanneled over the platforms 16. Correspondingly, the bowl 48 has amaximum depth less than about the maximum height of the bulge 46. InFIG. 2, the isoclines have been labeled with arbitrary numbers from thereference zero surface, with the bulge 46 increasing in height to anexemplary magnitude of about +6, with the bowl 48 increasing in depth toa maximum depth of about −5, and the purge trough 38 blending with thebowl 48 and onto the blend area 40 of the platform 16 and having amaximum depth of about −3.

These exemplary numbers are merely representative of the changingcontour of the scalloped platform 16. The actual magnitudes of the purgetrough 38, the bulge 46 and the bowl 48 will be determined for eachparticular design, with the maximum depth of the purge trough 38 rangingfrom 10 to 45 mils and the bowl ranging from about 37 to about 64 milsand the height of the bulge 46 ranging from about 40 mils (1 mm) toabout 450 mils (11 4 mm) for turbine airfoils ranging in height from 5cm to about 7.5 cm.

FIGS. 2 and 4 also illustrate that the purge trough 38 is generallysemi-spherical tangentially against the purge cavity, and moreparticularly in the blend area 40 of the platform 16, and generallyconcave laterally from its origin of maximum depth which is positioneddirectly in and extending across the blend area 40 of the platform 16between the leading edge 24 and the suction side 22 of the airfoil 14.The purge trough 38 extends aft toward the trailing edge 26 to blend ortransition smoothly into the bowl 48 when present. The bulge 46 isgenerally semi-spherical against the pressure side 20 of the airfoil 14,and generally convex both forwardly toward the leading edge 24 and inthe aft direction towards the trailing edge 26. In the axial planeextending circumferentially between the leading edges 24 of the airfoilrow, the bulges 46 are conical in section between the convex forward andaft portions thereof in the exemplary embodiment illustrated in FIG. 4for which computational flow analysis predicts a significant reductionin vortex strength and migration. The exemplary bowl 48 illustrated inFIGS. 2 and 5 is generally concave laterally from its origin of maximumdepth which is positioned directly on the suction side of each airfoil14 and blending with the purge trough 38. The bowl 48, like the bulge46, is generally semi-spherical, but concave centering on the airfoilsuction side 22.

FIGS. 2 and 4 illustrate the transition between the purge trough 38 andthe bowl 48 on the airfoil suction side 22, and the elevated bulge 46 onthe airfoil pressure side 20. More specifically, the bulge 46 configuredaft of the leading edge 24 on the pressure side 20, decreases gradually,along the longer extent of the pressure side 20 to the trailing edge 26.The gradual transition of the bulge 46 to the trailing edge 26 forms aridge extension of the bulge 46 that decreases in elevation.

Correspondingly, the purge trough 38 and the bowl 48 increase in depthgradually toward the leading edge 24 of the airfoil 14 and onto theblend area 40 to form an inlet for the purge flow 15. The purge trough38 and the depressed bowl 48 blend with the elevated bulge 46 graduallyalong the longer extent of the suction side 22 aft to the trailing edge26 as best illustrated in FIGS. 2 and 3.

FIGS. 2 and 5 illustrate that purge trough 38 blends into the bowl 48which decreases in depth along the suction side 22 from its peak depththat extends from the purge trough 38 near the blend area 40 of theplatform to near the airfoil hump toward the trailing edge 26. The bulge46 decreases continuously in height along the pressure side 20 from itspeak height aft of the leading edge 24 to the trailing edge 26. Both thebulge 46 and bowl 48 blend together around the trailing edge 26 andterminate laterally or circumferentially in the corresponding flowpassages 36 between the trailing edges 26 at the zero referenceelevation.

FIGS. 2 and 4 illustrate that the purge troughs 38, beginning orcommencing preferably forward of the leading edges 24 and transitioninginto the bowls 48 and the bulges 46 beginning or commencing preferablyaft of the leading edges 24, form or define laterally therebetween anaxially arcuate flute or channel 42 along the zero elevation contourtherebetween. The fluted channel 42 extends axially along the individualplatform 16 between adjacent airfoils 14 commencing forward of theleading edges 24 and terminating at the trailing edges 26, or aftthereof as desired within the available surface space of the platforms16.

The zero elevation contours may be a single line, or a land of suitablewidth between the bulge 46 and the bowl 48. In the land embodiment, theconvex bulge 46 preferably blends with one side of the land through aninflection region having a concave transition with the land. The purgetrough 38 and concave bowl 48 preferably blends with the other side ofthe land through another inflection region having a convex transitionwith the land.

Since the exemplary turbine stage illustrated in the Figures isconfigured as a turbine rotor stage, the individual platforms 16 areintegrally joined to the root of each airfoil 14, with a correspondingdovetail 18 (FIG. 2) therebelow, with the platforms 16 collectivelydefining the radially inner boundary or endwalls for the combustion gasflow 12. Each platform 16 therefore adjoins an adjacent platform at anaxial splitline 56, with the splitlines 56 bifurcating or splitting theinter-airfoil bowls 48 axially between the leading and trailing edges24, 26 in complementary first bowl portions 52 and second bowl portions54. This is best illustrated in FIG. 2 in which the platform 16 hasportions extending from the opposite pressure and suction sides 20, 22of the airfoil 14. The bulge 46 is disposed primarily on the pressureside 20 of the platform 16. The suction side portion 22 of the platform16 includes the first bowl portion 52 extending over most of theplatform 16 surface and extending into the blend area 40 of the purgecavity to form the purge trough 38.

However, the first bowl portion 52 is interrupted by the axial splitline56 from the complementary second bowl portion 54 integrally formed withthe bulge 46 on the pressure side 20 of the next adjacent platform 16.The first bowl portion 52 on one platform 16 is complementary with thesecond bowl portion 54 on the next adjacent platform 16 and collectivelydefine a single complete blended purge trough 38 and bowl 48 extendingfrom the suction side 22 of one airfoil 14 to the bulge 46 and its ridgealong the pressure side 20 of the next adjacent airfoil 14.

The axial splitlines 56 interrupt the circumferential continuity of theentire turbine row stage, and permit the individual fabrication of eachturbine blade in a conventional manner, such as by casting. The overallconfiguration of the turbine blade including its airfoil 14, platform 16and dovetail 18 may be cast in a conventional manner, and the scallopedfeatures thereof may also be integrally cast therein where feasible.

Alternatively, the platforms 16 may be cast with nominal axisymmetricplatforms with locally elevated material for the bulge 46, which maythen be machined using conventional electrical discharge machining (EDM)or electrochemical machining (ECM) for forming the 3D contour of thescalloped platform 16, including the final contours of the purge trough38, the bulge 46 and the bowl 48.

Since the gradient lines of the bowl portions 48 on the suction side 22of the airfoil 14 as illustrated in FIG. 2 run generallycircumferentially, the 3D bowl contours may be altered to 2D contoursvarying linearly in the circumferential direction for more readilypermitting casting thereof using conventional casting die halves, ifdesired.

A significant feature of the scalloped platforms 16 illustrated in FIGS.2 and 4 is the purge trough 38 provided extending into the blend area 40of the purge cavity and extending aft to blend with the bowl 48.Preferably each purge trough 38 is configured extending laterallybetween the leading edges 24 of adjacent airfoils 14, and moreparticularly between the leading edge 24 and suction side 22 of theairfoil. In an alternate embodiment, the purge troughs 38 may beconfigured to extend laterally forward the leading edge 24 of an airfoiland extending in a lateral position to just forward a decreasing aspectof the bulge 46 of the adjacent airfoil 14 to the suction side 22 of theairfoil (described presently). The purge troughs 38 rapidly blend withthe corresponding bowl 48 that extends over the large majority of thesuction side 22.

The purge troughs 38 provide a decrease in mixing of the purge flow 15and the core flow 13, thereby minimizing a subsequent downwash of thecore flow 13 on the pressure side 20 to backfill with fluid and weakenthe formation of horseshoe vortices at their inception. The purgetroughs 38 further modify the cross-passage static pressure gradientthat provides energy to the horseshoe vortices. The elevated bulge 46,configured directly aft of the leading edge 24, provides additionalweakening of the horseshoe vortices. Preferably each bulge 46 extends inmost part from aft of the leading edge 24 and in an aft direction alongthe pressure side 20 to the trailing edge 26.

The contour of each airfoil 14, and twist or angular position thereof,are selected for each design application so that the leading edge 24 ofthe airfoil 14 first receives the combustion gases 12, typically at anoblique angle from the axial centerline axis, and the purge flow 15,keeping it close to the platform 16 surface as it lifts off the platform16 on the suction side 22. The combustion gases 12, as the core flow 13,and purge flow 15 turn as they flow through the curved flow passages 36between the airfoils 14. The natural stagnation point of the incomingcombustion gases 12 may be aligned with the leading edge 24 itself oraligned closely adjacent thereto on either the pressure or suction sides20, 22 of the airfoil 14.

Accordingly, for each particular design application, at least one of thepurge trough 38 or the bulge 46 may be centered at the naturalstagnation point proximate the leading edge region of the airfoil 14.The so positioned purge trough 38, bulge 46 and complementary bowl 48are specifically introduced in the radially inner platforms 16 of theturbine rotor blades 10 to cooperate with each other with synergy forreducing the mixing of the purge flow 15 with the core flow 13 andmodifying the cross-passage static pressure gradient that drives thehorseshow vortices towards the airfoil suction side 22, thereby reducingthe strength of the horseshoe vortices that stretch and wrap around theleading edge 24 and flow downstream through the flow passages 36.

The combination of reduced losses due to secondary flows, vortexstrength and altered pressure gradients reduce migration of the vorticestowards the airfoil suction side 22, and reduce the tendency for thevortices to migrate along the airfoil 14 span for correspondinglyreducing losses in turbine aerodynamic efficiency.

Another exemplary embodiment is depicted in FIGS. 6 and 7. Each of thesefigures is similar to that of FIGS. 1 and 2, respectively, discussedabove. However, in each of illustrated FIGS. 6 and 7, in addition to thepurge trough 38, the bulge 46, and the bowl 48, a trailing edge ridge 50is configured at the trailing edge 26 of the airfoils 14 Similar to thebulge 46 discussed previously, the trailing edge ridge 50 is a bulged orscalloped platform which rises upwardly (+) into the flow passage 36from the platforms 16 which define the radially inner endwalls. It isadditionally noted, that in the illustrated embodiment of FIGS. 6 and 7,the purge trough 38 is configured having a maximum depth at the leadingedge 24, and more particularly at approximately 0% of the passage 36width “x” (described previously) and extends into both the blend area 41and onto at least a portion of the purge cavity wall 41. It should beunderstood that in an alternate embodiment a purge trough 38 configuredas described in FIGS. 2-6 is anticipated in conjunction with thetrailing edge ridge 50 described.

In the embodiment depicted in FIGS. 6 and 7 the trailing edge ridge 50is shown in a configuration having the purge trough 38, bulge 46 and thebowl 48. However, in another embodiment only purge trough 38 and thetrailing edges ridge 50 is present. In a further exemplary embodiment,the trailing edge ridge 50 is coupled with one of the bulge 46 formationor the bowl 48 formation. The present disclosure is not limited in thisregard as the combination of scalloped surfaces employed are selectedfor particular operational and design parameters, such as mass flowrate, etc.

Similar to the discussion regarding the bulge 46, the trailing edgeridge 50 rises into the flow passage 36. As shown by the contour linesadjacent the trailing edge 26, in FIG. 7, the slope of the trailing edgeridge 50 is steeper than that of the bulge 46. However, in otherexemplary embodiments the slope can be similar to, or less than, that ofthe bulge 46.

Further, in an exemplary embodiment, the structure of the trailing edgeridge 50 closest to the trailing edge 26 has the steepest slope, whereasas the distance from the trailing edge 26, along the platform 16,increases the slope decreases and becomes more gradual, thus providing amore gradual and smooth transition to the platform 16 surface.

The presence of the trailing edge ridge 50 may modify the loading of theairfoil 14 near the endwall. This modification can result in increasedlift, an alteration of the horseshoe and secondary flow structures, achange in the shock structures and accompanying losses, as well as amodification of the heat transfer.

By blending the trailing edge ridge 50 into the trailing edge 26 of theairfoil 14 and the platform 16, an increase in the aerodynamicefficiency of the airfoil 14, and thus turbine as a whole, can beachieved. Namely, the trailing edge ridge 50 can act to increase thearea for aerodynamic loading of the airfoil forming the airfoil 14. Byadding to the area that can support loading, the operational performanceof the turbine can be increased, resulting in more work being extractedfrom the turbine. Stated differently, the inclusion of the trailing edgeridge 50, of this embodiment, can act to extend the camber line of theairfoil 14 near the endwall. Thus, additional loading beyond thetrailing edge 26 can be supported. The aerodynamic effect of thisadditional loading acts as an overcambering of the airfoil 14, whereendwall loading is reduced near mid-passage of the airfoil 14 but isincreased near the trailing edge 26. Thus, near endwall velocities areslower, overturning is enhanced and the primary turbine flow shiftstoward the mid-span section. The result of this effective overcamber isa reduction in skin friction and secondary flow. Thus, an overcamberingeffective is achieved in the turbine without modifying the entireairfoil 14.

Additionally, the presence of the trailing edge ridge 50 allows for themanipulation of the operational thermal profile at the trailing edge 26of the airfoil 14. This is because the modification in secondary flow(discussed above) can change or cause a reduction of convective mixingand/or heat transfer which can normally bring the hot core flow 13 incontact with the endwalls. The trailing edge 26 of the airfoil 14 can bethe location of high temperature concentrations, thus limitingstructural performance of the blade 10 and the endwall at the trailingedge 26. The inclusion of the trailing edge ridge 40 allows formanipulation of the thermal profile. Thus, a desired thermaldistribution can be attained and can be optimized, resulting in areduction of the cooling required.

The shape and scalloped contour of the trailing edge ridge 50 inconjunction with the purge trough 38, whether employed in conjunctionwith bulges 46 and/or bowls 48, is determined to optimize performance ofthe airfoils 14 and the turbine. For example, the shape of the trailingedge ridge 50 is optimized either for aerodynamic performance ordurability or both, depending on the desired performance parameters andcharacteristics.

As shown in FIGS. 6 and 7 the trailing edge ridge 50 directly adjoinsthe trailing edge 26 of the airfoil 14. Further, in the embodiment shownin these figures, the trailing edge ridge 50 adjoins both the airfoilsuction side 22 and the pressure side 20. In another embodiment, thetrailing edge ridge 50 adjoins and extends from the trailing edge 26 asshown and adjoins only one of the pressure side 20 or the suction side22, depending on design and operational parameters. In a furtheralternative embodiment, the trailing edge ridge 50 adjoins and extendsfrom the trailing edge 26 as shown but does not adjoin either of thepressure side 20 or the suction side 22.

In a further exemplary embodiment, an additional bowl and/or bulge (notshown) may be positioned on the surface 16 at some point downstream ofthe trailing edge ridge 50. In such an embodiment, the bowl and/or bulgecan aid in vortex suppression or otherwise optimizing the operationaland performance parameters of various embodiments of the presentdisclosure.

In the embodiment shown in FIGS. 6 and 7 the maximum height (i.e.,positive (+) displacement above platform 16) of the trailing edge ridge50 is at the trailing edge 26, and the height of the trailing edge ridge50 reduces as the trailing edge ridge 50 extends away from the airfoil14 surfaces. The trailing edge ridge 50 smoothly transitions into thesurface 16 so as to affect efficient structural and thermal loaddistribution. In an embodiment where the purge trough 28, the trailingedge ridge 50 and either one, or both, of the bulge 46 and bowl 48scalloped surfaces are present, the trailing edge ridge 50 smoothlytransitions to these surfaces and the reference surface as optimized fordesign and performance purposes.

In an embodiment when included is the trailing edge ridge 50 and thebulge 46, the maximum height of the trailing edge ridge 50 may matchthat of the bulge 46, which has a maximum height which is generallyequal to the thickness of the incoming boundary layer of combustiongases 12 (see discussion previously). However, it is contemplated thatbased on varying operational parameters the height of the trailing edgeridge 50 can be higher than, or lower than, the height of the bulge 46.

In an exemplary embodiment, as with the purge trough 38, the bulge 46and the bowl 48, the trailing edge ridge 50 joins the root end of theairfoil 14 and trailing edge 26 with a fillet type structure suitable toprovide the needed structural integrity and performance.

As discussed previously, in an embodiment, the platforms 16 areintegrally joined to the root of each airfoil 14. Manufacturing of anembodiment with a purge trough 38 and a trailing edge ridge 50 asdescribed above can be similar to manufacturing methods discussedpreviously. Namely, the overall configuration of the turbine bladeincluding its airfoil 14, platform 16, and dovetail 18 may be cast in aconventional manner, and the scalloped platform including at least thepurge trough 38 and the trailing edge ridge 50 may be integrally casttherein where feasible. Alternatively, the platforms 16 may be cast withnominal axisymmetric platforms with locally elevated material for thetrailing edge ridge 50, which may then be machined using conventionalelectrical discharge machining (EDM) or electrochemical machining (ECM)for forming the 3D contour of the scalloped platform, including thefinal contours of the ridge. Of course, all other known and used methodsof manufacturing can be employed as the various embodiments of thepresent disclosure are not limited in this regard.

In an exemplary embodiment, the orientation of the trailing edge ridge50 is such that it follows the mean camber line for the airfoil shape.However, the present embodiment is not limited in this regarding as theorientation and overall shape of the trailing edge ridge 50 and itscontour is to be optimized such that the desired operational andperformance parameters are achieved. It is well within the ability of askilled artisan to perform such optimization.

The scalloped platforms have been disclosed above for a turbine rotor,but could also be applied to a turbine nozzle. In a turbine nozzle,turbine vanes are integrally mounted in radially outer and innerendwalls or bands which are typically axisymmetrical circular profilesaround the centerline axis. Both the inner and outer bands may bescalloped in a manner similar to that disclosed above for reducing theadverse effects of the corresponding secondary vortices generated at theopposite ends of the turbine nozzle vanes and increasing aerodynamicloading and efficiency while providing beneficial thermal distribution.

The scalloped platform 16 may therefore be used for enhancingaerodynamic efficiency in any type of turbine engine, and for any typeof turbine airfoil. Further examples include turbine rotor disks inwhich the airfoils are integrally formed with the perimeter of the rotordisk. Low pressure turbine blades may include integral outer shrouds inwhich the scalloped platform may also be introduced. Further, steamturbine blades and vanes may also include the scalloped platforms at thecorresponding root ends thereof. Additionally, various embodiments canbe employed in other similar applications such as pumps, blowers,turbines and the like. Embodiments as disclosed herein are not limitedin this regard.

Modern computer fluid dynamics analysis now permits the evaluation ofvarious permutations of the scalloped platforms 16 for minimizing mixingof a purge flow 15 and a core flow 13, while reducing vortices toincrease turbine efficiency. The specific contours of the purge troughs38, bulges 46, bowls 48 and trailing ridges 50 will vary as a functionof the specific design, but the form of the purge trough 38 extendinginto the blend area 40 of the purge cavity, the elevated bulge 46 on theairfoil pressure side 20 at the leading edge 24, the depressed bowl 48along the suction side 22 blending with the purge trough 38, and thetrailing edge ridge 50 at the airfoil trailing edge 26 will remainsimilar for specifically reducing the adverse effects of the mixing ofthe purge flow 15 with the core flow 13 and effects of vorticesgenerated as the combustion gases 12 split over the airfoil leadingedges 24, decreased aerodynamic loading and undesirable thermaldistributions.

In various embodiments, the purge troughs 38, bulges 46, bowls 48 andtrailing ridges 50 are blended with each other respectively and theairfoil 14 via fillet structures as described herein. For example, thepurge trough 38 and the bowl 48 will be blended to each other, as wellas the purge trough 38 and the bulge 46 being blended to each other withfillets while the trailing edge ridge 50 and the bowl 48 are blendedwith each other. It should be understood that the overall contours,blending and fillet structure can be optimized as needed.

While there have been described herein what are considered to bepreferred and exemplary embodiments of the present disclosure, othermodifications shall be apparent to those skilled in the art from theteachings herein, and it is, therefore, desired to be secured in theappended claims all such modifications as fall within the true spiritand scope of the disclosure.

1. A turbine stage comprising: a row of airfoils integrally joined tocorresponding platforms and spaced laterally apart to define respectiveflow passages therebetween for channeling gases, each flow passagehaving a width; each of said airfoils including a concave pressure sideand a laterally opposite convex suction side extending in chord betweenopposite leading and trailing edges; and at least some of said platformshaving a scalloped flow surface including a purge trough extendingtangentially into a blend area and at least a portion of a purge cavitywall of the platform and extending axially toward the suction side ofthe airfoil, aft of the leading edge, to channel a purge flow.
 2. Theturbine stage according to claim 1, wherein said purge trough isconfigured having a maximum depth laterally at a location −10%-60% ofthe width of the passage formed between the leading edges of adjacentairfoils, wherein such measurement is measured commencing from theleading edge of a first airfoil extending laterally toward the convexsuction side of the first airfoil and toward the leading edge of asecond adjacent airfoil at the concave pressure side of the secondadjacent airfoil.
 3. The turbine stage according to claim 2, wherein thepurge trough is configured having a maximum depth location at a positionaxially downstream of the leading edges and within the passage formedtherebetween.
 4. The turbine stage according to claim 2, wherein saidpurge trough is configured having a maximum depth laterally at alocation approximately midway between the leading edges of adjacentairfoils.
 5. The turbine stage according to claim 1, wherein said purgetrough is configured having a maximum depth axially at a locationforward the leading edge of the airfoil.
 6. The turbine stage accordingto claim 1, wherein at least some of said platforms include a bulgeextending along a portion of said airfoils and coupled to said at leastsome platforms, the bulges adjoining said pressure side aft of saidleading edge of each respective airfoil with the respective platforms.7. The turbine stage according to claim 1, wherein at least some of saidplatforms include a bowl extending along a portion of said airfoils andcoupled to said at least some platforms, the bowls adjoining said purgetrough and said suction side aft of said leading edge of each respectiveairfoil with the respective platforms.
 8. The turbine stage according toclaim 1, wherein at least some of said platforms include a trailing edgeridge structure extending along a portion of said airfoils and coupledto said at least some platforms, the trailing edge ridge structuresadjoining said pressure side, said suction side, and said trailing edgeof each respective airfoil with the respective platforms.
 9. The turbinestage according to claim 1, wherein at least some of said platformsfurther include: a bulge extending along a portion of said airfoils andcoupled to said at least some platforms, the bulges adjoining saidpressure side aft of said leading edge of each respective airfoil withthe respective platforms; and a bowl extending along a portion of saidairfoils and coupled to said at least some platforms, the bowlsadjoining said purge trough and said suction side aft of said leadingedge of each respective airfoil with the respective platforms, saidbulge and bowl form laterally therebetween an arcuate channel extendingaxially along said platform between adjacent airfoils.
 10. The turbinestage according to claim 9, further including a trailing edge ridgestructure extending along a portion of said airfoils and coupled to saidat least some platforms, the trailing edge ridge structures adjoiningsaid pressure side, said suction side, and said trailing edge of eachrespective airfoil with the respective platforms.
 11. The turbine stageaccording to claim 9, wherein said bulge and bowl terminate laterally insaid flow passage between said trailing edges.
 12. The turbine stageaccording to claim 9, wherein said bulge is centered at said pressureside aft of said leading edge, and decreases in height forward, aft, andlaterally therefrom and said bowl is centered at said suction side nearthe maximum thickness of said airfoils, and blends in a forwarddirection with said purge trough, and decreases in depth in an aftdirection and laterally therefrom.
 13. The turbine stage according toclaim 9, wherein said bulge decreases in height rapidly in a forwarddirection, aft of said leading edge and decreases gradually to saidtrailing edge and said bowl blends with said purge trough near saidleading edge and gradually to said trailing edge.
 14. The turbine stageaccording to claim 9, wherein said purge trough is concave laterally,said bulge is convex forward and aft, and said bowl is concavelaterally.
 15. A turbine stage comprising: a row of airfoils integrallyjoined to corresponding platforms and spaced laterally apart to definerespective flow passages therebetween for channeling gases, each flowpassage having a defined width; each of said airfoils including aconcave pressure side and a laterally opposite convex suction sideextending in chord between opposite leading and trailing edges; at leastsome of said platforms having a scalloped flow surface including a purgetrough extending tangentially into a blend area and at least a portionof a purge cavity wall of the platform, a bulge adjoining said pressureside aft of said leading edge, and a bowl adjoining said purge troughand said suction side aft of said leading edge of said respectiveairfoils, the purge trough extending axially toward the suction side ofthe airfoil to blend with the bowl and channel a purge flow.
 16. Theturbine stage according to claim 15, wherein at least some of saidplatforms having a trailing edge ridge structure extending along aportion of said airfoils and coupled to said at least some platforms,the trailing edge ridge structures adjoining said pressure side, saidsuction side, and said trailing edge of each respective airfoil with therespective platforms.
 17. The turbine stage according to claim 15,wherein said purge trough is configured having a maximum depth laterallyat a location −10%-60% of the width of the passage formed between theleading edges of adjacent airfoils, wherein such measurement is measuredcommencing from the leading edge of a first airfoil extending laterallytoward the convex suction side of the first airfoil and toward theleading edge of a second adjacent airfoil at the concave pressure sideof the second adjacent airfoil.
 18. The turbine stage according to claim17, wherein the purge trough is configured having a maximum depthaxially at a position axially downstream of the leading edges and withinthe passage formed therebetween.
 19. The turbine stage according toclaim 15, wherein said purge trough is configured having a maximum depthlaterally at a location forward the leading edge of the airfoil.
 20. Theturbine stage according to claim 15, wherein said bulge is centered atsaid pressure side aft of said leading edge, and decreases in heightforward, aft, and laterally therefrom and said bowl is centered at saidsuction side near the maximum thickness of said airfoils, and blends ina forward direction with said purge trough, and decreases in depth in anaft direction and laterally therefrom.
 21. A turbine blade comprising:an airfoil integrally joined to a platform, and having laterallyopposite pressure and suction sides extending in chord between axiallyopposite leading and trailing edges; and said platform including a purgetrough extending tangentially into a blend area and at least a portionof a purge cavity wall of the platform, the purge trough extendingaxially toward the suction side of the airfoil, aft of the leading edge,to channel a purge flow.
 22. The blade according to claim 21, furtherincluding a bulge adjoining said pressure side aft of said leading edge,a first bowl portion adjoining said purge trough and said suction sideaft of said leading edge, and a second bowl portion integrally formedwith said bulge on said pressure side and being complementary with saidfirst bowl portion to define therewith on an adjacent blade, acollective bowl.
 23. The blade according to claim 21, wherein at leastsome of said platforms having a trailing edge ridge structure extendingalong a portion of said airfoils and coupled to said at least someplatforms, the trailing edge ridge structures adjoining said pressureside, said suction side, and said trailing edge of each respectiveairfoil with the respective platforms.
 24. The blade according to claim21, wherein said purge trough is configured having a maximum depthlaterally at a location −10%-60% of the width of the passage formedbetween the leading edges of adjacent airfoils, wherein such measurementis measured commencing from the leading edge of a first airfoilextending laterally toward the convex suction side of the first airfoiland toward the leading edge of a second adjacent airfoil at the concavepressure side of the second adjacent airfoil.
 25. The blade according toclaim 24, wherein the purge trough is configured having a maximum depthaxially at a position axially downstream of the leading edges and withinthe passage formed therebetween.
 26. The blade according to claim 21,wherein said purge trough is configured having a maximum depth laterallyat a location forward the leading edge of the airfoil and the suctionside of an adjacent airfoil.